Question: The equation of a circle $C$ is $x^2+y^2+2x+14y+46 = 0$. What is its center $(h, k)$ and its radius $r$ ?
Explanation: To find the equation in standard form, complete the square. $(x^2+2x) + (y^2+14y) = -46$ $(x^2+2x+1) + (y^2+14y+49) = -46 + 1 + 49$ $(x+1)^{2} + (y+7)^{2} = 4 = 2^2$ Thus, $(h, k) = (-1, -7)$ and $r = 2$.